1. Field of the Invention
The present invention concerns external techniques to warm the human body for comfort, therapy, surgery, or other treatment. More particularly, the invention concerns a warm air blower that is mounted to the foot of a bed and utilized to direct warm air to the lower extremities of a supine person.
2. Description of the Related Art
Many people complain of having xe2x80x9ccold feetxe2x80x9d while laying in bed. For some people, they simply feel colder at any given temperature than other people. For others, the problem is more serious because they suffer from inadequate circulation to the legs and feet, resulting in abnormally cold feet and legs. In either case, the perception of cold feet can cause significant discomfort, especially while trying to sleep.
Normal body core temperature (xe2x80x9cnormothermiaxe2x80x9d) occurs at about 37xc2x0 Celsius. Body temperatures below this are considered xe2x80x9chypothermic,xe2x80x9d and have many negative physiological effects beyond mere discomfort. Temperature excursions of a mere 1-2xc2x0 Celsius below normal can profoundly affect many cellular and physiological functions in areas such as the immune system, coagulation system, cardiovascular system, and death rates during surgery. According to one published study, surgical patients with a core temperature of 34-35xc2x0 Celsius experienced three times more wound infections than persons maintained at 36xc2x0 Celsius.
Historically, the definition of xe2x80x9cnormothermiaxe2x80x9d has been limited to the core thermal compartment of the body. The peripheral thermal compartment, including the legs and other extremities, is designed to act as buffer or insulator between the core and the environment. Therefore, the peripheral compartment is expected to be hypothermic under many circumstances. This is one example of an xe2x80x9cevolutionary tradeoff.xe2x80x9d Namely, in order to maintain their core temperatures within a narrow range, warm blooded animals readily sacrifice warmness of the extremities.
This natural tendency toward peripheral hypothermia is exacerbated by vascular disease, which further reduces blood flow to the extremities. In fact, the combination of sacrificial hypothermia of the extremities and peripheral vascular disease can result in especially profound hypothermia of the legs. Persons with vascular insufficiency of the legs generally have colder legs, sometimes even approaching room temperature. These same persons are also prone to chronic non-healing skin wounds on their legs. These wounds may originate for various reasons, such as diabetes causing small vessel disease, external pressure causing local vascular occlusion, venous disease, and circulatory insufficiency reducing the blood flow and changing the hydrostatic gradients.
Whether peripheral hypothermia results from vascular disease, sacrificial hypothermia, or both, this condition inhibits important cellular functions of leg tissue. These cellular functions are not any different, or less important, than functions of cells in core vital organs. For example, a circulating immune cell does not know if it is fighting an infection in the heart or lungs, or the big toe. However, the extremities are more often hypothermic than the core vital organs, and therefore suffer more frequently from hypothermia-induced limitations.
Hypothermia in the lower extremities, then, is especially prevalent due to sacrificial hypothermia, peripheral vascular disease, or a combination of both. Peripheral hypothermia causes pain and possible interference with cellular functions of leg tissues.
Broadly, the present invention concerns a warming system, mounted to the foot of a bed, to warm a person""s lower extremities by directing air into the space between the mattress and overlaying blankets. The system utilizes a blower to direct air into an elongated, air permeable, fluid distribution chamber. The chamber is mounted at the foot of the bed, and spans the bed from side to side so that air exiting the chamber warms the person""s feet. For maximum thermal transfer, the chamber is placed beneath blankets and other layers that cover the person, but above any lower layers such as a mattress cover and fitted sheet. Various embodiments of the chamber are contemplated, such as a length of open cell foam, a hollow manifold that is naturally air permeable, air impermeable hollow manifold with many punctures or other tiny distribution apertures, collapsible tube, etc. While the person is lying in bed beneath the blankets, with feet proximate the foot of the bed, the blower directs temperature-regulated air into the chamber; when the air exits the chamber, it warms the person""s feet. Temperature is regulated to provide an infusion of warmed air.
As discussed above, one embodiment of the invention may be implemented to provide an apparatus to manage temperature in a supine person""s legs and feet. A different embodiment concerns a method to manage temperature in a person""s lower extremities.
The invention affords its users with a number of distinct advantages. For example, the invention relieves or even prevents the discomfort of xe2x80x9ccold feetxe2x80x9d by directing normothermic air at a person""s peripherally hypothermic lower extremities. Additionally, by applying heat to the legs, the invention encourages blood flow to the legs by virtue of sympathetic vasodilation and local temperature-mediated vasodilation. The invention is also believed to prevent some leg and foot ulcers from forming by maintaining the lower extremities at a near normal temperature during sleep.
Moreover, by warming the feet and legs during the sleep hours, the present invention is believed to help provide improved healing of chronic ulcers of the leg or foot that have resulted from vascular insufficiency of the legs. Recent experiments have shown promise for healing chronic wounds by warming them from a typically hypothermic state toward normothermia. Warming the wound toward a normothermic temperature helps enable normal cellular functions that are inhibited by hypothermia. As proposed by the present inventors, severely hypothermic wounds are believed to exist in a state of xe2x80x9csuspended animation,xe2x80x9d where the cells are alive but inactive. Severe hypothermia causes cell division (xe2x80x9cmitosisxe2x80x9d) to stop, enzyme and biochemical reactions to be slowed or stopped, cell membrane functions to be altered, and the immune system to be inhibited. The result is that wounds are slow to heal, if ever. Thus, by gently warming the peripheral extremities, the present invention contributes to the healing of chronic wounds that would otherwise linger due to hypothermic interference.
In contrast to other arrangements such as heating blankets, the invention focuses heated air primarily on persons"" feet and lower legs. As the face and torso are sensitive to temperature, many people do not tolerate additional heat applied to the body during sleep. In fact, some people might turn a heating blanket off because they feel too warm, yet their legs and feet are still hypothermic. In contrast, people tolerate more heat applied to the legs than the body and face before complaining of feeling too warm. People with diabetes and vascular disease are even more heat tolerant, because they tend to lose sensation in their feet and legs. The present invention capitalizes upon these facts by focusing heat upon the lower extremities.
As another benefit, in the case of people with vascular disease, diabetes, or another condition causing poor circulation in the peripheral extremities, the invention preferably regulates the temperature of warming air to about 38xc2x0 Celsius. This temperature is normothermic since it approximately coincides with the upper limit of the body""s normal core temperature. The approach of this invention diverges from electric blankets and other known heating devices, which typically apply a hyperthermic temperature to a person in order to develop a temperature gradient. By using a normothermic temperature, the invention helps avoid thermal injuries such as burns, which can occur without a person""s knowledge because of the reduced sensory perception in the peripheral extremities. By limiting the temperature of warming air to about 38xc2x0 Celsius, the invention can still induce a sufficient temperature gradient to induce warming because a peripherally hypothermic person""s feet and legs are colder than normal. While approximately 38xc2x0 Celsius is the preferred air temperature, it should be noted that temperatures higher and lower than 38xc2x0 Celsius are also contemplated. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.